"""
#############################################################################
implement client and server-side logic to transfer an arbitrary file from
server to client over a socket; uses a simple control-info protocol rather
than separate sockets for control and data (as in ftp), dispatches each
client request to a handler thread, and loops to transfer the entire file
by blocks; see ftplib examples for a higher-level transport scheme;
#############################################################################
"""

import sys, os, time, _thread as thread
from socket import *

blksz = 1024
defaultHost = 'localhost'
defaultPort = 50001

helptext = """
Usage...
server=> getfile.py  -mode server            [-port nnn] [-host hhh|localhost]
client=> getfile.py [-mode client] -file fff [-port nnn] [-host hhh|localhost]
"""

def now(): 
    return time.asctime()

def parsecommandline():
    dict = {}                        # put in dictionary for easy lookup
    args = sys.argv[1:]              # skip program name at front of args
    while len(args) >= 2:            # example: dict['-mode'] = 'server'
        dict[args[0]] = args[1]
        args = args[2:]
    return dict

def client(host, port, filename):
    sock = socket(AF_INET, SOCK_STREAM)
    sock.connect((host, port))
    sock.send((filename + '\n').encode())      # send remote name with dir: bytes
    dropdir = os.path.split(filename)[1]       # filename at end of dir path
    file = open(dropdir, 'wb')                 # create local file in cwd
    while True:
        data = sock.recv(blksz)                # get up to 1K at a time
        if not data: break                     # till closed on server side
        file.write(data)                       # store data in local file
    sock.close()
    file.close()
    print('Client got', filename, 'at', now())

def serverthread(clientsock):
    sockfile = clientsock.makefile('r')        # wrap socket in dup file obj
    filename = sockfile.readline()[:-1]        # get filename up to end-line
    try:
        file = open(filename, 'rb')
        while True:
            bytes = file.read(blksz)           # read/send 1K at a time
            if not bytes: break                # until file totally sent
            sent = clientsock.send(bytes)
            assert sent == len(bytes)
    except:
        print('Error downloading file on server:', filename)
    clientsock.close()

def server(host, port):
    serversock = socket(AF_INET, SOCK_STREAM)     # listen on TCP/IP socket
    serversock.bind((host, port))                 # serve clients in threads
    serversock.listen(5)
    while True:
        clientsock, clientaddr = serversock.accept()
        print('Server connected by', clientaddr, 'at', now())
        thread.start_new_thread(serverthread, (clientsock,))

def main(args):
    host = args.get('-host', defaultHost)         # use args or defaults
    port = int(args.get('-port', defaultPort))    # is a string in argv
    if args.get('-mode') == 'server':             # None if no -mode: client
        if host == 'localhost': host = ''         # else fails remotely
        server(host, port)
    elif args.get('-file'):                       # client mode needs -file
        client(host, port, args['-file'])
    else:
        print(helptext)

if __name__ == '__main__':
    args = parsecommandline()
    main(args)
